[R] Time data

[Petr Pikal]

Hi


On 20 Dec 2005 at 11:12, Marc Bernard wrote:

Date sent:      	Tue, 20 Dec 2005 11:12:28 +0100 (CET)
From:           	Marc Bernard <bernarduse1 at yahoo.fr>
To:             	r-help at stat.math.ethz.ch
Subject:        	[R] Time data

> Dear All, I wonder how to compute the age from the date of birth and
> the date of examination. Suppose that have the following data:
> 
>   df <- as.data.frame(rbind(c(1,"10/08/1950","15/03/1998"),
>   c(1,"10/08/1950","20/07/1998"), c(1,"10/08/1950","23/10/1998")))
> 
>   names(df) <- c("ID", "date_birth", "date_exam")
> 
>   where:
>   date_birth: is the date of birth
>   date_exam: date of examination
> 
>   I used the following program to compute the value of the age  :
> 
>   difftime(strptime(as.character(df$date_exam), '%d/%m/%Y'),
>   strptime(as.character(df$date_birth), '%d/%m/%Y'))/365.25
> 
>   which gives me as an output:
> 
> > Time differences of 47.59491, 47.94251, 48.20260 days
> 
>   theses values are actually the 3 ages (but 
> 
>   My questions are:
> 
>   1- Why in the output it says "days" instead of "years")

this is in attributes of an output and is not changed by calculations

> 
>   2- How can I obtain the output as a numeric vector, without the
>   statement "Time difference of ....". This is in order to use it in
>   my calculations.

as.numeric(as.Date(df$date_exam)-as.Date(df$date_birth))/365

However you can use it in calculations without problem as I suppose 
that "Time difference of" results from print method of a difftime 
object.


> 
>   3- Is there a way quicker and less redondant  to compute the age
>   form the date_birth and date_exam?

as.Date(df$date_exam)-as.Date(df$date_birth)

HTH
Petr


> 
>   Thanks a lot,
> 
>   Bernard,
> 
> 
> 
> ---------------------------------
> 
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Petr Pikal
petr.pikal at precheza.cz